Declare #[rustc_pub_transparent] attribute

Author: GrigorenkoPV

compiler/rustc_feature/src/builtin_attrs.rs

@@ -641,6 +641,11 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         ErrorFollowing, EncodeCrossCrate::Yes,
         "rustc_deprecated_safe_2024 is supposed to be used in libstd only",
     ),
+    rustc_attr!(
+        rustc_pub_transparent, Normal, template!(Word),
+        WarnFollowing, EncodeCrossCrate::Yes,
+        "rustc_pub_transparent is supposed to be used in libstd only",
+    ),
 
 
     // ==========================================================================

compiler/rustc_span/src/symbol.rs

@@ -1672,6 +1672,7 @@ symbols! {
         rustc_private,
         rustc_proc_macro_decls,
         rustc_promotable,
+        rustc_pub_transparent,
         rustc_reallocator,
         rustc_regions,
         rustc_reservation_impl,